This invention relates to optical devices, and more particularly to optical waveguide devices.
In the integrated circuit industry, there is a continuing effort to increase device speed and increase device densities. Optical devices are a technology that promise to increase the speed and current density of the circuits. In long-distance waveguide applications such as fiber optic transmission lines, optical signals are often transmitted using multiple polarizations to convey information relating to a single signal. An optical media can have different propagation constants for different polarizations of light, different polarizations of light can be conveyed at different velocities. Therefore, the different polarizations can temporally separate over long distances. If the polarizations separate sufficiently, one polarization from one signal can interfere with another polarization from another signal. Polarization controllers are devices that maintain the temporal spacing of the different light polarizations to limit such interference between polarizations. Polarization controllers can be formed from multiple passive element, with each passive element made from glass or clear plastic or alternatively from a semiconductor material, such as silicon.
Polarization controllers, as with most optical devices, are susceptible to changes in such operating parameters as temperature, device age, device characteristics, device age, device characteristics, contact, pressure, vibration, etc. As such, the various components of the Polarization controllers are typically contained in packaging that maintains the parameters as desired. Providing such packaging is extremely expensive. Even if such packaging is provided, passive polarization controllers may be exposed to slight condition changes. Passive polarization controllers perform differently under different conditions. For example, different bandwidths of light will be attenuated to different levels depending on the conditions. If the characteristics of a passive polarization controller is altered outside of very close tolerances, then the optical polarization controller will not adequately perform its function. In other words, there is no adjustability for passive polarization controllers.
As such it would be desirable to provide an optical polarization controller that can controllably measure distances or motions using one or more light bandwidths. Additionally, it would be desirable to provide a mechanism to compensate in polarization controllers for variations in the operating parameters such as temperature and device age.
The present invention is directed to an optical polarization controller apparatus and associated method that controls a first temporal separation between a first polarization and a second polarization of an output optical signal, wherein a second temporal separation exists between a first polarization and a second polarization of an input optical signal. The optical polarization controller comprises a controller, a polarization separation device, and a delay element. The controller determines the first temporal separation. The controller compares the first temporal separation with the second temporal separation. The polarization separation device transmits the first polarization of the output optical signal along a first path and transmits the second polarization of the output optical signal along a second path. The delay element delays the first polarization of the output optical signal relative to the second polarization of the output optical signal whereby a duration of the first temporal separation becomes closer to a duration of the second temporal separation. The delay element further comprising a gate electrode and a voltage source. The gate electrode has a prescribed electrode shape positioned proximate the waveguide. The voltage source is connected to the gate electrode for applying voltage to the gate electrode, wherein the voltage causes the gate electrode to project into the waveguide the region of changeable propagation constant, said region of changeable propagation constant corresponding generally in shape to the prescribed electrode shape. The controller controls the propagation constant level of the region of changeable propagation constant by varying the voltage applied to the gate electrode wherein changing the propagation constant level of the region of changeable propagation constant changes a duration that the first polarization of the output optical signal is delayed within the region of changeable propagation constant.